Biosensors for pesticides - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 32

modifi ed AChE, and other enzymes were also employed in construction of biosensors.
The main drawback of AChE amperometric biosensors is that the enzymatic product,
thiocholine oxidation, needs a high applied potential, which reduces the stability of the
biosensor. To solve this problem mediators such as 7, 7 -tetracyanoquinodimeth-

ane (TCNQ) [7] and highly conductive materials such as carbon nanotubes [8] have
been employed. To avoid enzyme purifi cation and reduce the cost, whole cells have
also been directly interfaced with transducer surface. The major limitation with enzyme
inhibition-based pesticide determination is non-selectivity. To improve the selectivity
of the pesticide biosensors, immunosensors have been introduced, where antibodies
act as recognition receptors. Several detection methods have been interfaced with bio-
sensors/immunosensors such as potentiometric, amperometric, differential pulse vol-
tammetry (DPV), chemiluminescence, piezoelectric, surface plasmon resonance, etc.
for the improvement of the biosensor analytical performance [9]. The sensitivity of
the biosensor and stability of the biocatalyst are mainly governed by the immobiliza-
tion method adopted for the interfacing of the biocatalyst with the transducer surface.
Several immobilization methods such as covalent linking, adsorption and entrapment
have been developed. Furthermore the exploitation of advanced microfabrication tech-
nology allows the design of portable, easy-to-use, inexpensive and environmental
friendly biosensor chips and strips for pesticide monitoring in real samples. Although
pesticide biosensor technology has been progressing dramatically, commercialization
is still in its infancy and needs more research.

, 8, 8

2.1.3 Thrust areas for pesticide biosensors
Pesticide biosensors are highly useful in agriculture, the food industry and the medi-
cal sector. In the export and import of food materials portable biosensors or kits with
quick responses are highly convenient for fast detection. Similarly if the biosensor
has the capability to detect the pesticide/toxicant selectively present in clinical sam-
ples, it would be highly advantageous for diagnosis and treatment in the medical sec-
tor. Miniaturized sensor strips or kits are highly advantageous and applicable for the
domestic applications to check the water quality for daily use.

2.2 BIOCATALYSTS USED IN PESTICIDE BIOSENSORS

The selectivity and sensitivity of biosensors are governed by the biocatalyst. Commonly
used biocatalysts in biosensors are enzymes [10, 11], antibodies [12, 13], whole cells
[14], and artifi cial receptors such as molecularly imprinted polymers [15, 16].

2.2.1 Enzymes used in pesticide biosensors and their features
Most of the pesticide biosensors are designed based on the inhibitory property of
enzymes. AChE and butyrylcholinesterase (BChE) are widely used in the develop-
ment of pesticide biosensors [17, 18]. Inhibition leads to a decrease in activity, which